A law-based approach also seemed to offer the advantage of being a relatively
straightforward and uncontroversial way to deal with both the terrorist
acts that demanded an immediate response and those activities that created
a longer- term terrorist threat. Relevant U.S. laws included garden-variety
proscriptions of homicide, expansive definitions of criminal conspiracy,
specialized federal legislation addressing terrorism, war crimes, and
hijacking dating back to the 1970s and expanded after September 11, most
notably to widen proscriptions on harboring anyone whom one knows or has
reason to believe is an active terrorist, providing material support to
terrorist organizations or engaging in conspiracies to commit terrorism.8

Activities and individuals outside the United States could be brought
legally within the reach of the U.S. criminal justice process. American
law enforcement, prosecutors and courts have long adopted a broad construction
of U.S. statutes’ extraterritorial reach, particularly where Congress
explicitly so provides, as it has in the case of antiterrorism legislation.
Accepted doctrines of international law permit a state to enact laws punishing
non-citizens’ overseas behavior where only part of a complex offense takes
place in the state claiming jurisdiction. Other international legal principles
may permit a state to prohibit and sanction actions threatening its security
or harming its nationals, even though undertaken by foreigners abroad.
Further, the intentional targeting of massive numbers of civilians in
the September 11 attacks, the particular methods of destruction deployed,
and the prior declaration by apparently responsible parties of a “war”
against the United States all support the claim that this new strain of
terrorism counts among the handful of offenses—including war crimes, crimes
against humanity, piracy, hijacking, and sometimes international terrorism—that
any state may reach and punish, without regard to where they occur.9
Moreover, international law arguably permits a state to enact and apply
retroactively laws punishing such universally condemned crimes.10